1. Field of the Invention
The invention relates to a transparent laminate, in particular a laminate which inhibits puncture by projectiles, which has a chemically prestressed pane having a thickness d, a compressive stress of the surface CS, a penetration depth of the prestressed layer DOL and a tensile stress in the interior CT.
2. Description of Related Art
Transparent protection against the effect of ballistic projectiles, for example against gun ammunition and shrapnel, is produced from glass plates or panes which are laminated together by means of polymer films or pourable resin layers. As glass material, use is generally made of soda-lime glass and in the case of relatively thick composites low-iron soda-lime glass because of the required transmission. The protection action of the composites is determined and classified by standardized methods, as are presented by way of example in the specifications STANAG 4569 and DIN 1063 or VPAM APR 2006. STANAG 4569 provides, for example for protection class 3, a test using hard-core ammunition of the calibre 7.62×51 having a tungsten carbide core and of the calibre 7.62×54R having a steel core. Furthermore, the effect of grenade shrapnel is tested by means of a test using 20 mm “fragment-simulating projectiles” (FSP). This impact has to be withstood by the composite so that the projectiles neither pass through nor are particles which could cause injury or significant damage to persons or objects to be protected behind the protective facility released by the protective facility.
A reduction in the weight per unit area of the transparent protection can be achieved by, for example, partial or complete replacement of the glass plates composed of soda-lime glass by at least partially crystalline materials such as glass-ceramic, transparent ceramics or crystalline materials such as sapphire.
However, for cost reasons, the high-priced transparent ceramics which are highly effective in providing protection and other crystalline materials are barely used.
A critical factor for use in vehicles is, apart from sufficient protective effect, a very low weight per unit area of the composites since this represents part of the total weight of the vehicle and any weight improvement thus makes it possible to increase the useful load of the vehicle. In general, transparent protective facilities are arranged in the upper region of the vehicle, i.e. above its centre of gravity. This leads to a low weight of the transparent protection also being able to improve the travelling stability on poor roads and when travelling around curves.
Further critical factors for use in vehicles are good emergency vision properties which make it possible to see through the pane to a restricted extent even after breakage of one or more panes.
DE 10 2008 043 718 A1 describes tank glazing comprising at least one outward-facing transparent glass-ceramic pane (a) which has a thickness in the range 3-20 mm, optionally at least one pane (b) selected from the group consisting of borosilicate glass, soda-lime glass and aluminosilicate glass and having a thickness in the range 3-20 mm, which can be chemically prestressed, and at least one transparent polymer pane (c), in particular polycarbonate pane, facing the object to be protected, where the thickness of the pane (c) is in the range from 3 to 15 mm; the individual panes are joined by transparent intermediate layers composed of pourable resin or polymer films. This tank glazing has, inter alia, the disadvantage of high costs caused by the glass-ceramic pane used.
DE 692 27 344 T2 discloses transparent safety glazing for aircraft, which comprises a chemically prestressed glass pane which faces the interior and is provided with a splinter protective layer composed of PU on its side facing the cabin, a 4 mm thick, outer glass pane and a PVB intermediate layer which consists of 7 layers and has a total thickness of about 4 mm and is arranged between outer and inner glass pane.
US 2007/0060465 A1 discloses a chemically prestressed lithium aluminosilicate glass which has a high resistance to breakage in the event of impact of high-velocity projectiles, where the glass is characterized by a compressive stress in the surface of at least 100 000 psi and a depth of the compressively stressed region of at least 600 microns. In the document, it is stated that the glass offers a very high resistance to breakage. Arrangement of the glass pane in a laminate is not discussed.
Finally, WO 2011/120680 discloses a transparent facility for protection against impact, projectiles, shrapnel or pressure waves, which comprises at least four brittle panes, with a chemically prestressed, brittle pane being arranged at a distance of from 6 mm to 20 mm from the exposed side.